The invention relates to a driver assistance system of a non-track-bound vehicle which, by applying a steering torque to the driver's steering wheel, makes a direction-oriented steering recommendation to the driver by way of an electric motor or the like. Concerning the technical environment, reference is made by way of example only to European Patent Document EP 1 777 143 B1.
Such a known driver assistance system can make a haptic steering recommendation to the driver by way of the steering wheel in certain driving situations, for example, when driving on the autobahn, in the case of a passing maneuver necessary for maintaining a driving speed predefined by the driver and appropriately controlled by a cruise control system. For this purpose, an appropriately activated motor (servomotor) applies a directed steering torque of a suitable amount to the driver's steering wheel, which has the purpose of leading to a change of the steering wheel angle set so far, and finally of initiating a passing operation controlled by the driver by use of his steering wheel. The amount of steering torque applied by the above-mentioned motor or by the driver assistance system is usually selected such that the driver will always be able to oversteer this steering torque and thereby overrule the system default. The action upon the steering wheel by such a steering torque representing the steering recommendation can take place in different fashions, thus, for example, in the form of a rectangular pulse of a predefined pulse height and time period or in the form of an at first linearly rising, then briefly constant, and subsequently linearly falling steering torque, or also by way of a steering torque function that is non-linear with respect to time. All these and similar forms are to be considered as falling within the scope of a torque applied in the sense of a “direction-oriented steering recommendation.”
When the amount, i.e. the extent, and the time period of the steering torque representing a steering recommendation is selected such that the driver sufficiently notices this haptic signal, the driver, if he sufficiently firmly holds his steering wheel with his hands, will considerably dampen the brief steering impulse of the vehicle resulting from this steering torque, so that solely as a result of the assistance system almost no deviation of the vehicle from the original course will take place. However, if the driver holds the steering wheel only slightly, for example, only with one hand, or the driver has even completely removed his hands from the steering wheel (hands off), the steering impulse that is applied by the driver assistance system and is hardly damped, despite the relatively short time period, leads to a considerable deviation of the vehicle orientation from the original driving trajectory. If, in such a case, the driver does not want to comply with the recommendation of the driver assistance system, thus, for example, because the neighboring driving lane, into which a change is recommended by the driver assistance system, at least in the driver's estimation, is not sufficiently vacant, at least the driver's reaction time will go by before the latter can correct this unwanted course.
It is an object of the present invention to provide a remedial measure for the above-described problems.
For a driver assistance system of a non-track-bound vehicle which, by applying a steering torque to the driver's steering wheel by way of an electric motor or the like, makes a direction-oriented steering recommendation to the driver, the solution of this object is characterized in that, by means of this steering torque, first a steering wheel angle in the recommended rotating direction at an angular speed that is greater in its amount is set or at least is to be set and that subsequently a steering wheel angle is set or at least is to be set in the opposite rotating direction at an angular speed that is lower in its amount.
First, it should be pointed out that a driver assistance system and, therefore, an electronic control unit is described herein, by which the described process is carried out or can be carried out. The process applies a steering torque to the driver's steering wheel of a non-track-bound vehicle by use of an electric motor or the like. In this case, by way of this steering torque, a direction-oriented steering recommendation is made to the driver. Such an electronic control unit for a driver assistance system includes a processor and appropriately programmed memory to carry out its functions.
In accordance with the present invention, in view of the fact that, on the one hand, a reliable awareness of the steering recommendation by the driver is to be ensured even if the latter is holding the steering wheel tight, and simultaneously in the event that the driver is not or is barely holding the steering wheel, no excessive deviation of the orientation of the vehicle from its original driving trajectory should take place, a quasi-automatic countersteering (with an opposite rotating direction) is provided with respect to the precedingly given steering recommendation (or its rotating direction). This automatic countersteering is preferably initiated by the same motor which also applies the steering torque representing the steering recommendation to the steering wheel, and this countersteering should be noticeable to the driver at the steering wheel as little as possible or should at least be significantly less noticeable than the preceding steering recommendation.
In this sense, it becomes possible to apply to the steering wheel corresponding steering torques differing with respect to their amount noticeable to the driver, or at least its time-dependent courses, thus, different so-called steering torque functions. The above-mentioned steering recommendation can therefore be made by a jerky application of a steering torque to the driver's steering wheel, and subsequent to this steering recommendation (in the form of a steering torque), a steering torque of a lower amount and a correspondingly longer duration, which is directed against this steering torque and at least approximately neutralizes it, can be applied to the steering wheel. In a preferred embodiment, the amount of the integral of the steering torque representing the steering recommendation over its effective period can essentially be identical to the amount of the integral of the at least approximately neutralizing steering torque over its effective period, so that, at least with respect to the steering torque initiated within the scope of the steering recommendation, a complete neutralization will take place; however, the orientation of the vehicle itself is not yet corrected thereby. As stated in detail below, the latter can subsequently also be carried out automatically, preferably proportioned such that this is not interpreted by the driver as a further steering recommendation.
The application of corresponding steering torques or steering torque functions as such is, however, only a special embodiment of the present invention; more generally, the present invention can be described by a suitable activation of the motor (servomotor, electric motor) representing these steering torque functions in that certain steering angles, here called steering wheel angles, are set or at least are to be set at the driver's steering wheel, at different setting speeds, i.e. different angular speeds (as a mathematical derivation of the steering wheel angle over the time). The latter, specifically the desired setting of a steering wheel angle, applies to a case in which the driver holds his steering wheel so tight that, by means of sensibly dimensioned servomotors, no steering torque can be applied that is so high that a corresponding steering wheel angle can actually be set. Independently of the force by which the driver holds his steering wheel, however, a change (even if only a slight change) of the steering angle at an angular speed greater in its amount is haptically noticeable in a best-possible manner to the driver and is particularly significantly more noticeable than a (preferably even slight) change of the steering wheel angle at an angular speed that is lower in its amount.
If the driver is holding his steering wheel with an extremely low force or if he is not at all holding onto the steering wheel, a steering recommendation in the form of a change of the steering wheel angle taking place at an angular speed greater in its amount can also be visually perceived in a best-possible manner by way of the steering wheel movement or by means of a change of the orientation of the vehicle. However, even if the driver is tightly holding on to his steering wheel, a change according to the invention of the steering wheel angle at a greater angular speed is at least haptically clearly noticeable to the driver because, with a correspondingly high steering torque for the representation of this angular speed, at least a slight and therefore noticeable change of the steering wheel angle will occur. In contrast, the subsequent change of the steering wheel angle according to the invention at a considerably lower angular speed in the rotating direction opposite the previously made steering recommendation, irrespective of how tightly the driver is holding his steering wheel, is hardly noticed by the driver, specifically neither haptically nor visually.
The above explanation also indicates a particular advantage of the process according to the invention, which is carried out by a driver assistance system according to the invention. Specifically, this process can be implemented in an automatically self-controlling fashion, with the force applied to the steering wheel by the driver being the disturbance variable. When this force is very low, the steering torque applied to the steering wheel by the above-mentioned motor or the corresponding time-related steering torque function may be of a low amount, whereas, when the driver is holding his steering wheel in a very strong manner, a corresponding steering torque function of a higher amount of the maximal steering torque can be applied to the steering wheel in an automatically controlled fashion.
In that, as basically suggested, when implementing the process according to the invention, the driver assistance system rotates the steering wheel, at first at a higher angular speed and therefore clearly noticeably to the driver, about a certain, although possibly only small angle into the direction coinciding with the steering recommendation and subsequently rotates the steering wheel at a lower angular speed and therefore at least less noticeably and preferably virtually not noticeably to the driver, back into the opposite direction, the effect of such a steering recommendation on the orientation of the vehicle (more precisely, of its longitudinal axis) will be less than in the state of art, in which only the steering recommendation is made but no subsequent automatic steering in the opposite rotating direction takes place. In this case, the steering wheel angle set at the lower angular speed and thereby at least less noticeably to the driver (in the opposite rotating direction) with respect to its amount, may be essentially equal to the steering wheel angle precedingly set at the greater angular speed and thereby more acutely noticeably to the driver. After the complete implementation of such a steering recommendation, the steering wheel will at any rate advantageously be situated back in its original angle position.
In accordance with an advantageous further development, it may be provided that, subsequent to the setting of the steering wheel angle having the opposite rotating direction, preferably also at a lower angular speed, a further steering wheel angle or at least a further steering angle acting upon the steerable wheels is set automatically, i.e. by the driver assistance system according to the invention, by which the vehicle is changed along a straight course of the road at least to the orientation held before the making of the direction-oriented steering recommendation. Not only the steering angle introduced into the steering system of the vehicle by the steering recommendation is quasi neutralized thereby but the steering impulse introduced into the steering system of the vehicle with this steering recommendation, with respect to the vehicle orientation, is advantageously automatically canceled, so that this steering recommendation only has the effect of a slight lateral offset of the vehicle with respect to the condition before this steering recommendation. This automatic targeted orientation of the vehicle preferably also takes place in a manner proportioned such that it is hardly or at least considerably less noticed than the steering recommendation previously generated at the steering wheel and applied to it in the form of a torque.
A driver assistance system according to the invention can interact particularly advantageously with a vehicle steering system, which is equipped with a superimposed system by which a further additional steering angle effective at the steerable wheels can be added to the steering angle predefined by the driver at the steering wheel, (compare in this respect, for example, DE 103 07 475 A1), whereby the gear ratio between the steering wheel and the steerable wheels can be changed. For a further improvement of the process according to the invention by way of such a superimposed system, when a direction-oriented steering recommendation is made by way of the steering wheel and during the subsequent automatic setting of a steering wheel angle in the opposite rotating direction, the superimposed system can in each case set an additional steering angle directed against the set steering wheel angle, so that the effect of the steering wheel rotating angle represented as a steering recommendation as well as of the subsequent slower rotating-back of the steering wheel according to the invention at the steerable wheels is reduced. As an alternative or in addition, for the further suggested orientation of the vehicle along a straight course of the road at least approximately into the orientation held before the making of the steering recommendation, an additional steering angle also suitable for this purpose can be set in the superimposed system.
A driver assistance system according to the invention can advantageously interact with a vehicle steering system, in which, in addition to the front wheels, which are steerable by way of the steering wheel, the rear wheels of the vehicle are at least also slightly steerable. Thus, when making a direction-oriented steering recommendation by way of the steering wheel and subsequently automatically setting a steering wheel angle in the opposite rotating direction, a steering angle at the rear wheels of the vehicles in the same direction can in each case be set, whereby the yaw movement of the vehicle is reduced and the vehicle is essentially offset slightly laterally, but essentially retains its original orientation (along a straight course of the road). Should the latter not be fully accomplished, as an alternative or in addition, for the further suggested orientation of the vehicle along a straight course of the road, at least approximately into the orientation held before the making of the steering recommendation, a steering angle suitable for this purpose can also be set at the steerable rear wheels of the vehicle.
A driver assistance system according to the invention can advantageously interact with a vehicle braking system, by which, independently of the steering system, a yaw moment can be impressed on the vehicle by one-sided braking, as occurs in the state of the art relating to the current electronic stabilization programs (ESP, DSC or electronic stability control). By interacting with such a system, when a direction-oriented steering recommendation is made by way of the steering wheel and, during the subsequent automatic setting of a steering wheel angle by one-sided braking, a yaw moment can be generated that is directed against the respective steering wheel angle, whereby the yawing movement of the vehicle is reduced and the vehicle is essentially slightly laterally offset but essentially retains its original orientation (along a straight course of the road). Should the latter not be completely accomplished, as an alternative or in addition, for the further suggested orientation of the vehicle along a straight course of the road, at least approximately into the orientation held before the making of the steering recommendation, a yaw moment suitable for this purpose can be also generated by one-sided braking.
It was mentioned above that, in the case of a driver assistance system according to the invention, the electric motor or servomotor applying the corresponding steering torque or torques for setting the abovementioned steering wheel angles to the steering wheel can be subjected to an automatic control by use of a closed automatic control circuit with respect to the steering torque function to be applied. In this case, the automatic control can be carried out with respect to certain steering wheel angles to be set at a different angular speed and with a different rotating direction. As an alternative, the respective angular speed, at which the steering wheel is rotated at least minimally, as a function of the present marginal conditions, particularly as a function of the force with which the driver is holding the steering wheel, can be automatically controlled to certain predefined values. However, as an alternative, a control (pre-control) may also be provided such that certain time-related steering torque functions are provided for the above-mentioned electric motor/servomotor, during whose implementation, for the making of a direction-oriented steering recommendation, first a steering-wheel angle is set in the recommended rotating direction at an angular speed whose amount is greater, and subsequently a steering-wheel angle is set in the opposite rotating direction at an angular speed whose amount is lower.
In the case of a driver assistance system according to the invention, when the electric motor or servomotor is applying the corresponding torque or torques to the steering wheel, possible friction effects in the pertaining steering system of the vehicle are taken into account in a suitable manner; i.e. particularly friction losses which reduce the effect noticeable to the driver at his steering wheel can be taken into account when activating the above-mentioned servomotor such that the driver, as desired, can clearly recognize the steering recommendation, whereas the subsequent “countersteering” for the at least partial neutralization of the steering operation acting upon the vehicle from this steering recommendation is virtually not or at least considerably less noticeable or recognizable to the driver.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.